The invention relates to an rf generator for magnetic resonance imaging apparatus, comprising a modulator in which a carrier is modulated with an envelope signal, and also comprising a transmitter stage which is connected subsequent to the modulator.
An rf generator of this kind is known from DE-OS 36 05 547 corresponding to the commonly owned U.S. Pat. No. 4,843,549. Therein, the envelope signal is amplitude modulated on the carrier. The subsequent transmitter stage serves as a linear amplifier for the amplitude modulated carrier. The same holds good for the rf generator described in the earlier European application 88 200 981 which corresponds to commonly owned U.S. Pat. No. 4,879,514. Therein, the modulator has a digital construction but the amplifier is coupled thereto via a digital-to-analog converter. Amplifiers of this kind must deliver an output power of from a few hundred W to some kW. The modulated carrier frequency then amounts to from 5 MHz to approximately 200 MHz, depending on the strength of the magnetic field of the magnetic resonance imaging apparatus in which the rf generator is used. Such amplifiers are expensive.